Optical transmitter modules used in optical networks for transmitting optical data signals come in a variety of configurations. A typical optical transmitter or transceiver module has a TOSA that includes at least one laser diode and various other electrical components. A laser driver circuit of the module, which can be either external to or internal to the TOSA, outputs an electrical drive signal to each respective laser diode to cause the respective laser diode to be modulated. When the laser diode is modulated, it outputs optical signals that have power levels corresponding to logic is and logic Os. An optics system of the module couples the optical signals produced by each respective laser diode into the end of a respective transmit optical fiber held within an optical connector module that connects to the optical transmitter or transceiver module.
One well known type of optical communications module is a transistor outline (TO)-can assembly. A typical TO-can assembly includes a header and a cap. The header and the cap are typically made of a metallic material, such as stainless steel, for example, to allow them to be welded together. The TO-can assembly is generally cylindrical in shape. The header has an upper mounting surface on which the components of the TOSA are mounted, including a laser diode and other electric components, such as the laser diode driver circuitry. The components of the TOSA are electrically interconnected with proximal ends of electrical leads that pass through the header and have distal ends that are disposed on the opposite side of the header for electrically interconnecting the TOSA to external electrical circuitry, such as electrical circuitry of a printed circuit board (PCB).
TO-can assemblies are typically not used in WDM applications that use more than two wavelengths for a number of reasons. One reason is that TO-can packages are relatively bulky in size and shape and, therefore, are not well suited for incorporating multiple sets of discrete optics and other components that are needed for transmitting optical data signals of multiple wavelengths. Planar lightwave circuits (PLCs), also known as photonic integrated circuits (PICs), are better suited for WDM applications because they allow many optical, optoelectronic and electrical components to be integrated on the same substrate and packaged in a relatively small package. PLCs, however, require special equipment to manufacture them, which leads to large capital investments for plant retooling and time delays in bringing the products to market.
Although it is known to package bi-directional optical subassemblies (BOSAs) in TO-can packages, the existing BOSAs are only capable of using two wavelengths and therefore have only two TO-can devices. It is also known to make three-channel, or tri-, OSAs that have three TO-can devices. The BOSA and tri-OSA packages are also relatively large in size. In addition, due to the configuration of the focusing optics they employ, the known BOSAs and tri-OSAs are limited to having a wavelength spacing between the TO-can devices that is greater than 10 nanometers (nm), which limits the wavelengths that can be used by the BOSAs and tri-OSAs. The focusing optics system configuration also limits the number of channels and wavelengths to three at most due to limitations on the ability of the focusing optics to achieve a great enough focal length if more than three TO-can devices are included. Due to all of these limitations, the existing BOSAs and tri-OSAs are not practical for use in applications that require smaller packaging or in applications that require more than two or three wavelengths.
Cloud computing and next generation data center applications are driving very large demands for increased bandwidth and low-cost compact packaging. A need exists for a WDM TOSA assembly that is capable of transmitting optical data signals having more than three wavelengths and that can be packaged in relatively low-cost compact packages.